IR Visa - How long do my wife and step-daughter have to remain in America?

they can leave as soon as they like. Green cards are issued to allow people to live primarily in the US. they aren't some sort of permanent tourist visa. What was the point of going to all the trouble and expense if they didn't want to actually live in the US? as noted, even if they don't spend over 12 months outside of the US at any point, they can still lose their green card status if they continually spend most of the year outside of the US.

If you prefer to spend most of your time in your home country, then you're likely to lose your "permanent" residency here. Permanent residency is supposed to be just that, permanent. As LPR's you're required to spend most of your time here. Prolonged stays outside the country require advanced approval from ICE. Keep spending long amounts of time, say several months at a time, in your home country and you may come back to find that Immigration will deem your green cards abandoned.

John, sorry to hear that you made that mistake. Verbal abuse is just as bad as physical abuse. I have lived in her shoes. You were tearing down her dignity. It's a great thing that you sought help, but for the most part, when a woman has been abused long enough, she really starts to hate you for all of the yelling and cursing and unfortunately for you, she has simply had enough and there is no chance to re-kindle the relationship. Not to mention the divorce has been finalized. If she refuses to talk to you, maybe you could mail her a letter and let her know that you have tried to correct the problem through counseling and let her know how much you miss them. More than likely, for her it's over. Just remember for the next lady that comes into your life how this behavior is not appropriate for anyone. That's the problem with men these days, they have no respect for women.

Then as soon as they arrive file a I-131 for a Re-enry permit ...

wait for that then they can leave for two years